Pneumatic tire

ABSTRACT

A pneumatic tire and a method of constructing a tire bead for the same, in which the tire has a bead portion which is reinforced by a bead core of wire running around the bead portion and the wire is housed in a circular elastomeric support which forms a cradle in which the wire is located. The bead can be made by winding wire around the preformed elastomeric cradle.

This invention relates to pneumatic tires and to a method of making atire bead, particularly for heavy duty truck tires.

A typical tire has a bead core which is manufactured by coating wire inrubber compound and winding the wire on a die to form a hoop of bundledtogether wire, the bundle typically having a generally hexagonal, agenerally round or a generally square cross-section and being known inthe trade as a bead bundle. Sometimes the bead bundle is held in shapeby spirally winding a wrapping cord around the outside of the bundle.However, the bead bundles may become distorted during the manufacture ofa tire, for example, the cross-section of the bead core in the tire maybe altered from being square to become rhomboid during the tirebuilding.

The present invention seeks to provide a means of constructing a morestable tire bead assembly.

Accordingly there is provided a method of making a tire bead assemblyincluding the step of forming a substantially circular support ofelastomeric material and which has a substantially `U`-shaped radialcross-section having the channel therein directed radially outwardly ofthe circular support, and then combining said support with a bead corecomprising a plurality of turns of wire bundled together, so as to lodgethe bead core within the channel.

Also according to the invention there is provided a pneumatic tirehaving a bead portion for seating on a wheel rim, said bead portionbeing reinforced by a bead core of wire extending circumferentiallyaround the bead portion, said wire being housed within a circularelastomeric support which extends around the bead core and which forms acradle in which the wire is located.

Preferably the cradle support has a substantially `U`-shaped radialcross-section and the wire is lodged within the arms of the `U`.

DESCRIPTION OF DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a partial radial cross-section through a bead portion of atire according to this invention.

FIG. 2 an enlarged radial cross-section through a bead assembly and itssupport as are utilised in FIG. 1.

FIG. 3 is a schematic representation of one method of manufacturing thebead assembly.

FIG. 4 is a schematical representation of and alternate method of makingthe cradle.

DETAILED DESCRIPTION

In FIG. 1 there is shown a radial section through the bead portion 11 ofa carcass of a heavy duty pneumatic tire. The carcass is reinforced by arubberized ply 12 of nylon or polyester cords. The reinforcing ply 12passes around the axially inner side of a bead assembly 13 and has a plyturn up portion 14 which extends up the axially outer side of the beadarea. (The terms axially inner and axially outer refer to axial positionrelative to the mid-circumferential plane of the tire). The bead portionhas an internal surface 15 which could be lined with an air impermeablelayer.

The bead assembly 13 (see FIG. 2) comprises a circular support 16 thatextends continuously around the bead portion 11 of the tire and a beadcore 20 of wire reinforcement 17 which also extends continuously aroundthe bead portion. The support 16 has a substantially `U`-shaped radialcross-section with the arms 18 of the support 16 being directed radiallyoutwardly of the tire to provide an annular channel or recess 19therebetween which faces radially outwardly of the circular support. Thechannel 19 is of a substantially square cross-section and the support 16has an outer surface 23 which is substantially circular having a radiusR struck from a point P at the center of the channel. The sides 21 andbase 22 of the channel 19 each have a respective height h or width Wthat is substantially equal to the radius R of the outer surface 23. Thechannel 19 is substantially filled with the bead core 20 which comprisesa single rubber coated wire 17 wound into adjacent hoops which arebundled together within the channel 19 of the support 16. Because thebead core 20 is lodged within the support, it allows for a close packingof the bead wire 17 as the bead 20 is formed by winding the wire 17around the support 16.

In the present embodiment of the invention, the support 16 is made froman extrudable polyurethane elastomer of a hardness in the range shore A70-100 at 20° C., a density range of 1.2-1.3 grm/cm³, and a tensilestrength of 300-500 kg/cm². Such a material is marketed under the tradename DESMOPAN by Bayer Chemicals.

Now with reference to FIG. 3, the bead assembly 13 may be made asfollows, the polyurethane DESMOPAN is processed in an extruder 25 and anextrudate 26 of the desired cross-section, as illustrated for thesupport 16 in FIG. 2, is passed through a cutter 27 and cut to length.The cut-to-length extrudate 26 is formed into a hoop-like support 24 bywelding the ends of the extrudate 26 together so that the channel 19faces radially outwards. The bead core 20 is formed by winding singlefilament wire 17 around the polyurethane support until the channel 19 isalmost filled. The channel 19 need not necessarily be filled and asingle profile could be used more than one size of tire e.g. 900 R 20and 1000 R 20 use the same profile. The completed bead assembly 13 isthen used on the tire manufacture in the conventional manner.

As an alternative to winding a single filament wire around the support,a layer comprising a plurality of parallel wire filaments could be woundinto the channel around the support.

If it is necessary to improve the adhesion between the polyurethanesupport and the rubber of the tire carcass, the cut-to-lengthpolyurethane extrudate 26 can be treated by leaching its surface to givesome microporosity and then coating it with an adhesive for example anadhesive marketed under the tradename CHEMLOK 218 by Hughson Chemicals.

Instead of forming the polyurethane support 16 from a hooped extrudate24 it is possible to inject or cast liquid polyurethane resin into amold 31 having a cavity therein of the required shape. The resin curesto form a solid casting or molding. This process is called reactioninjection molding. Typical cast polyurethanes are marketed as two partsystems, a glycol and an isocyanate, for example VULKOLLAN and DESMODURmarketed by Bayer Chemicals.

An advantage of the tire construction described in this specification isthat the increased overall dimensions of the bead assembly 13 result inthe carcass reinforcing ply 12 lying closer to the natural equilibriumcurve of the tire.

In another method of assembly also according to this invention, the wireis wound around a metal former to form a bead bundle, as is previouslyknown. The preformed circular support is then deformed and snapped intoplace around the bead bundle utilizing the elastomeric properties of thesupport.

While certain embodiments and details have been shown for the purpose ofillustrating the invention it will be apparent to those skilled in theart that various changes and modifications can be made therein withoutdeparting from the scope of the invention.

I claim:
 1. A tire wherein the support has a radial cross-section suchthat the channel therein has a substantially square cross-section andthe outer surface of the support has a substantially circularcross-section.
 2. A pneumatic tire comprising a bead portion for seatingthe tire on a wheel rim, said bead portion having a bead assemblytherein comprising a circular support that extends continuously aroundsaid bead portion and a bead core of wire reinforcement which alsoextends continuously around the bead portion, said support having asubstantially U shaped radial cross section with the arms of the supportdirected radially outwardly of the tire to provide an annular channeltherebetween which faces radially outwardly of the circular support,said bead core being disposed within said channel, said supportcomprising a polyurethane elastomer having a hardness of Shore A 70-100at 20° C.